Generally, parasitosis is caused by infestation of host animals with parasites such as unicellular protists (protozoa), multicellular helminths and arthropods. It is reported that the incidence of parasitosis in advanced countries has been remarkably decreased by improvement of environmental hygiene, but on a global scale, particularly in developing countries, parasitosis still widely prevails and causes tremendous damage.
In recent years, even in advanced countries, there has been an increasing trend in the incidence of parasitosis. This is partly because of introduction of infection sources via long- or short-term overseas travelers, and partly because of parasitic infection due to ingestion of food imports, frozen foods, raw meat, fish meat, etc. or via domestic animals and pets. Another problem is that immunodeficiency caused by mass administration of immunosuppressants, anticancer drugs, etc. or by AIDS etc. allows usually non-pathogenic or low-pathogenic parasites to express their pathogenicity and to cause opportunistic infection in hosts.
Further, parasitosis in domestic animals, such as pigs, horses, cattle, sheep, dogs, cats and domestic fowls, is a universal and serious economic problem. That is, parasitic infection of domestic animals causes anemia, malnutrition, debility, weight loss, and serious damage of intestinal tract walls, tissues and organs, and may result in decline in feed efficiency and productivity, leading to a great economic loss. Therefore, novel endoparasite control agents as a parasiticide, an antiprotozoal or the like have always been desired.
Certain kinds of carboxamide derivatives have been known to have microbicidal activity (see Patent Literature 1 to 13). Further, it is known that certain kinds of carboxamide derivative are effective against nematodes that may damage agricultural products (see Patent Literature 4 or 5). However, Patent Literature 1 to 13 has neither description nor suggestion that the disclosed compounds are effective against endoparasites in animals such as mammals and birds.
Furthermore, it has been reported that compounds that inhibit succinate-ubiquinone reductase (mitochondrial complex II), which is one of the respiratory enzymes of endoparasites, can serve as an endoparasite control agent (see Non Patent Literature 1), but it has been unknown whether carboxamide derivatives have inhibitory effect on succinate-ubiquinone reductase (mitochondrial complex II). Further, Patent Literature 1 to 13 has neither description nor suggestion on any inhibitory activity of the disclosed carboxamide derivatives on succinate-ubiquinone reductase (mitochondrial complex II).